1. Field of the Invention
The present invention relates to a capacitor-built-in-type printed wiring substrate. More particularly, the invention relates to a capacitor-built-in-type printed wiring substrate on which an IC chip or IC-chip-carrying printed wiring substrate is mounted while connection terminals formed on the capacitor and those formed on the printed wiring substrate are connected to the IC chip or IC-chip-carrying printed wiring substrate, as well as to a capacitor-built-in-type printed wiring substrate capable of being connected to an IC chip or IC-chip-carrying printed wiring substrate. Also, the invention relates to a printed wiring substrate and a capacitor for use in the capacitor-built-in-type printed wiring substrate.
2. Description of the Related Art
With advancement of integrated-circuit technology, the operating speed of an IC chip has increased, potentially involving malfunction caused by superposition of noise on, for example, a power line. As a measure for eliminating noise, as shown in FIG. 30, a chip capacitor 3 is mounted on an upper surface 2A or on a lower surface 2B of a printed wiring substrate 2 on which an IC chip 1 is mounted. Capacitor connection lines 4 to be connected to two electrodes of the capacitor 3 are disposed in the printed wiring substrate 2. The chip capacitor 3 is connected to the IC chip 1 via the capacitor connection lines 4 and flip-chip pads 5.
3. Problems to be Solved by the Invention
However, the above process requires a designer to previously reserve area for mounting of the chip capacitor 3, thereby lowering the degree of freedom in mounting of other electronic components and attachment of a reinforcing member for reinforcing the printed wiring substrate. Further, the presence of other circuit lines tends to cause the capacitor connection lines 4, which extend between the IC chip 1 and the chip capacitor 3, to become relatively long and thin. As a result, the resistance and inductance of the capacitor connection line 4 itself tend to increase, failing to sufficiently meet demand for low resistance and low inductance.
In order to cope with the above problem, a capacitor may be integrally formed in a printed wiring substrate. Specifically, resin insulation layers and wiring layers formed on both sides of a core substrate are partially utilized so as to form a capacitor structure in which a resin insulation layer serving as a dielectric layer is sandwiched between opposed wiring layers (electrode layers). However, in the event the capacitor becomes defective due to short circuit or defective insulation resistance, the entire value-added printed wiring substrate must be discarded, representing a considerable loss. Thus, the manufacturing cost of a printed wiring substrate increases. Moreover, even when high-dielectric-constant ceramic powder is mixed in, the specific dielectric constant of the resin insulation layer is generally 40 to 50 at the highest, and hence the built-in capacitor encounters difficulty in attaining a sufficiently large capacitance.
The printed wiring substrate may assume a size substantially equal to that of an IC chip. A CSP (chip scale package) is an example of such a printed wiring substrate. When the printed wiring substrate assumes the form of a CSP, the printed wiring substrate (CSP) on which an IC chip is mounted is itself mounted on another printed wiring substrate. Even in this case, a need to eliminate noise may arise. However, as in the case described above, the other printed wiring substrate encounters difficulty in carrying a chip capacitor while meeting demand for attainment of low resistance and low inductance or in forming therein a capacitor of large capacitance.
Also, for example, in order to enable insertion and connection of a printed wiring substrate having BGA-type terminals to a socket or through-holes of a motherboard or in order to ease thermal stress arising between the printed wiring substrate and the socket or motherboard, an interposer may be interposed between the printed wiring substrate and the socket or motherboard to thereby establish connection therebetween. Even when such an interposer is used, need to eliminate noise by means of a capacitor may arise.